This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Ferritins are a broad superfamily of iron storage and detoxifying proteins found in plants, mammals and many microorganisms. A novel ferritin was found in marine pennate diatoms, unicellular photosynthetic organisms that play a major role in global primary production and carbon sequestration in the deep ocean. Crystal structures of ferritin derived from the pennate diatom Pseudo-nitzschia multiseries (PmFTN) revealed the characteristic ferritin ferroxidase centres, monomeric fold and spherical assembly. Three metal sites (A, B, C) were identified from iron(II) and zinc(II) crystal soaking experiments and anomalous dispersion data. The observed iron and zinc atoms form a pathway leading towards the central cavity where the stored iron mineral is formed. Metal coordinating residues are hypothesized to gate the passage of iron from the ferroxidase site to nucleate the mineral core. We will determine crystal structures of variants of metal coordinating amino acids in the presence of iron(II) and to gain further insights into the iron storage mechanism of PmFTN.